1. Field of the Invention
The present invention relates generally to under-voltage release mechanisms and, more particularly, to a shock-resistant under-voltage release mechanism having a shock-resistant tripping device.
2. Background Information
Numerous types of circuit breakers are known and understood in the relevant art. A circuit breaker is typically configured to interrupt a circuit in response to a trip event (e.g., without limitation, an over-current condition; an under-voltage condition). Generally, circuit breakers include a moveable contact that is placed into electrical contact with a stationary contact to complete an electrical circuit. When desired, a tripping mechanism moves the moveable contact away from the stationary contact to interrupt the electrical circuit. Numerous types of tripping mechanisms are known.
In one type of tripping mechanism, for example, one or more trip buttons are provided which, when activated, cause a trip bar to rotate. Rotation of the trip bar causes an interruption mechanism to operate, thereby moving the moveable contact away from the stationary contact. The trip button(s) may be depressed manually, or by a plunger of a trip mechanism, or may be operated by other electrical apparatus as needed for the specific application. One such type of trip mechanism, for example, is an under-voltage release mechanism. An example of an under-voltage release mechanism may be found in U.S. Pat. No. 6,255,924 to Turner et al. which is incorporated herein by reference.
The under-voltage release mechanism employs a tripping device that includes a coil, a magnetically permeable core, and a magnetically permeable and movable plunger, as is generally known and understood in the relevant art. When the circuit breaker is in operation and the movable contact is engaged with the stationary contact, the coil of the tripping device is energized. A magnetic field is generated by the coil which causes the plunger to be biased against a spring. When the circuit voltage is greater than a given preset level, the magnetic field generated by the coil magnetically interacts with the plunger and overcomes the force of the spring such that the plunger is retained in a retracted position (i.e., the plunger is kept away from the trip button). When the circuit voltage drops below the given preset level, however, the magnetic field generated by the coil is insufficient to overcome the force of the spring. Accordingly, the spring biases the plunger into an extended position where the plunger engages the trip button, which, in turn, initiates rotation of the trip bar in order to interrupt the electrical circuit.
While generally effective, such under-voltage release mechanisms are unsuitable for some applications. For instance, circuit breakers employing such under-voltage release mechanisms may be subject to relatively high levels of shock-loading which cause such under-voltage release mechanisms to inadvertently and inappropriately trip the circuit breaker.
Thus, a need exists for an improved shock-resistant under-voltage release mechanism having a shock-resistant tripping device.